In the past it has been necessary for boiler operators to periodically discharge water from the boiler in order to flush the boiler of built up mineral deposits and impurities. Prolonged operation of a boiler without such blowdown of the boiler can result in mineral buildup in the boiler and in the related pipes, thereby substantially reducing the efficiency of operation of the boiler and eventually causing the pipes to be substantially restricted.
More recently, apparatus has been developed to provide for automated blowdown of boilers at selected intervals. An example of such apparatus is illustrated in the Anderson U.S. Pat. No. 3,908,605, issued Sept. 30, 1975.
Attention is also directed to the Cancilla et al. U.S. Pat. No. 3,802,398, issued Apr. 9, 1974; the McNeil et al. U.S. Pat. No. 3,668,838, issued Jun. 13, 1972; the Kensig U.S. Pat. No. 1,812,050, issued Jun. 30, 1931. Attention is also directed to the Madden U.S. Pat. No. 2,270,067, issued Jan. 13, 1942; the Holdt U.S. Pat. No. 4,070,992, issued Jan. 31, 1978; the Kelly U.S. Pat. No. 4,285,302, issued Aug. 25, 1981, and the Rice U.S. Pat. No. 2,597,597, issued May 20, 1952.
In an effort to control mineral buildup in boilers, it is common practice to add chemicals to the water going into the boiler in order to increase the tendency of the minerals to remain in a dissolved state and to thereby prevent collection of solids in the boiler or in the pipes of the heating system. These chemicals are added in amounts depending on the maximum level of dissolved solids existing in the water in the boiler.
In the prior art apparatus, it is common that the boiler will be subjected to blowdown on a timed sequence. During the period of time between blowdown operations, i.e., discharge of sediment from the boiler, the amount of dissolved solids in the water will increase from a relatively low value immediately following the blowdown step to a substantially higher value just prior to the next blowdown. During this time period between blowdowns, make-up water is added to the boiler, and the amount of minerals in the system is increased each time water is added. The amount of chemicals added to the make-up water is dependent on the maximum value of total dissolved solids in the water prior to blowdown. With the prior art apparatus, there is normally a substantial fluctuation in the amount of dissolved solids in the boiler water during each full blowdown cycle. To prevent accumulation of deposits in the boiler and the related conduits of the heating system, chemicals must be added in amounts sufficient to handle the content of the water in the boiler just prior to blowdown. If the fluctuations of the level of dissolved solids in the water go through a wide range, substantially more chemicals must be added to the water than are necessary if the range of the level of impurities is held within a narrowly controlled set of parameters.
Another feature of the prior art apparatus is that sediment commonly collects in the low water cut-off mechanism float chambers or water columns. If this sediment collection is sufficient to restrict the operation of the water columns or of the low water cut-off devices, it is possible that the water level in the boiler may reach an undesirably low level and cause damage to the boiler or even catastrophic failure.